Last winter’s near-record low monarch overwintering numbers caused no small alarm amongst monarch watchers.  

At the time, though, Monarch Watch Director Emeritus Chip Taylor cautioned that the monarch population is resilient and prone to large swings. So far, this year’s numbers are bearing out his optimism. 

 “It was easy to envision that, like in 2013 (the lowest population recorded at 0.67 ha), it would take several years for the population to recover. As expected, the early numbers of returnees were low, but they were early and that was a positive sign that the population might recover.”

 By mid-June, there was enough data for Taylor to write, “…the numbers indicate that the growth of the population this year is comparable to that of most populations since 2015. The recovery to this point is nothing short of extraordinary and is a testament to the monarch’s resilience.”

 From that point, Taylor casts an eye forward, to what the rest of the current migration may bring for monarch numbers. His analysis really gets down into the (milk)weeds. One of his main points, though, is that at every stage in the monarchs’ migration, weather and plant resources affect the numbers – whether for better or worse. The more high-quality sightings of monarchs we have now, the better our ability to predict their future population will be.

 When the number of hectares occupied by the overwintering colonies is really low, for instance – like last winter, or in 2013-14 – the monarchs still could have had a large population at the start of that year’s migration to Mexico. If weather conditions are favorable the following spring, they could also quickly rebuild their population – as seems to be happening this summer. 

 The amount of milkweed along the migratory routes probably puts an upper limit on the number of monarchs – which is why it’s important to protect, and plant more, milkweed. However, Taylor points out that weather can, and often does, prevent the population from reaching that potential maximum. In particular, 2023’s drought in Texas probably reduced the population during the southern migration, helping to explain why this past winter’s overwintering numbers were so low

 

How do they know all this? What else can I do to help?

 

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